A difference that no one is aware of?

In my "trapped in another world" fic, my character's first exposure to chess is after she arrives. What they are playing is closer to shatranj than what we think of as chess, and even then the names of the pieces are different.

Since there is no contrast in anyone's mind, is there a good way to show the difference? Should I just ignore the difference so that it's an in-joke for the few who get it?

I looked over it quickly on Wikipedia and there didn't seem to be an appreciable difference that you could instantly make a reader aware of. Even the pieces looked the same laid out on the board in the example they gave. I'd really not sweat this one - call it shatranj if you want - people might be glad to look it up and learn something.